This invention relates to filling of gas cylinders having a porous packing material with acetylene. More specifically, the invention relates to a process and apparatus for reducing the time required to fill the cylinders with acetylene.
Production of acetylene by hydration of calcium carbide and compression of the acetylene to fill cylinders containing acetone and a porous packing material is still practiced using methods developed prior to 1940. Improvements to cylinder packing materials and safety procedures have reduced the hazards associated with acetylene production, packaging, and transportation. The acetylene and acetone are safely retained by the packing material allowing for high volume storage of the acetylene at reduced total pressure. However, the production and filling processes are manually controlled over a period of at least about 20 hours from the start of acetylene production to complete filling of a reasonable number of cylinders. The long cycle time includes many hours of idle time waiting for the acetone to dissolve the acetylene.
As shown in FIG. 1 (Prior Art), filling of packed cylinders 10 with acetylene is typically achieved with a single speed or a two-speed compressor 12 which receives acetylene from a calcium carbide hydration unit 14. The acetylene is typically produced at a pressure less than 15 psig and is then passed through a heat exchanging cooler 16 to reduce the temperature of the acetylene gas to at least about 10.degree. C. The acetylene is then passed through a drier 18 to remove water and a purifier 20 to remove other contaminants. The acetylene is washed in a scrubber 22 prior to entering the compressor 12. The pressure of the acetylene is typically from 5 to 10 psig prior to entering the compressor 12. The acetylene must be compressed to a pressure of at least 250 psig to completely fill a packed cylinder 10. A high pressure drier 24 removes oil and condensed water from the pressurized acetylene. The compressed acetylene is held in a manifold 26 which has connections for a plurality of packed cylinders 10. The pressure of acetylene in the manifold 26 is controlled by shutting off the compressor 12 or switching to low speed if available. A cooling water supply 28 provides cooling water to the heat exchanging cooler 16 and excess cooling water 30 is often sprayed on the cylinders 10 for cooling of gas lines and the cylinders.
The number of cylinders 10 which can be filled at one time primarily depends on the volume capacity of the compressor 12 which account for most of the capital cost. Filling of the cylinders 10 typically begins with the compressor 12 set at 100% power. The acetylene pressure in the manifold 26 steadily rises to a pressure of about 350 psig while the acetylene slowly fills the cylinders. Diffusion of the acetylene into the cylinders is slow, but is enhanced by cooling the cylinders. Absent the packing material and the acetone, the cylinders would rapidly fill at 250 psig but would contain compressed acetylene at a much lower stability than dissolved acetylene at 250 psig. The manifold pressure is typically allowed to drop 100 psig before the compressor 12 is turned on again. Cycling of the compressor 12 continues until a lack of a significant pressure drop indicates that the cylinders are full. As the cycles are repeated, the compressor 12 is operated for progressively shorter time periods. The compressors 12 are very inefficient when operated for short intervals at 100% power. Thus two-speed compressors are typically switched to 50% speed when the compressor will not run long at 100% speed. Combining the compressing time and the idle time for all cycles, the time required to fill the cylinders to about 95% capacity is typically at least 20 hours for a reasonable amount of cylinders.
Repeated cycling of the one speed or two speed compressors 12 results in many hours of reduced demand or no demand for acetylene which limits production capacity. However, the high capital costs for the compressors 12 essentially results in acceptance of the production capacity which can be achieved with the available compressors. An increase in acetylene bottling capacity typically requires the purchase of additional compressors. Repeated cycling of the compressors also leads to high electric bills because of the high peak load required to start the compressor.
It is an object of the present invention to improve acetylene production by reducing the time needed to fill a reasonable number of packed cylinders. It is a further object of the present invention to reduce the frequent on/off cycling of acetylene compressors so that the process of filling packed cylinders with acetylene can be more easily controlled and frequent start-up of the compressors can be eliminated.